/guides/source/plugins.md
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- The Basics of Creating Rails Plugins
- ====================================
- A Rails plugin is either an extension or a modification of the core framework. Plugins provide:
- * a way for developers to share bleeding-edge ideas without hurting the stable code base
- * a segmented architecture so that units of code can be fixed or updated on their own release schedule
- * an outlet for the core developers so that they don’t have to include every cool new feature under the sun
- After reading this guide, you will know:
- * How to create a plugin from scratch.
- * How to write and run tests for the plugin.
- This guide describes how to build a test-driven plugin that will:
- * Extend core Ruby classes like Hash and String.
- * Add methods to ActiveRecord::Base in the tradition of the 'acts_as' plugins.
- * Give you information about where to put generators in your plugin.
- For the purpose of this guide pretend for a moment that you are an avid bird watcher.
- Your favorite bird is the Yaffle, and you want to create a plugin that allows other developers to share in the Yaffle
- goodness.
- --------------------------------------------------------------------------------
- Setup
- -----
- Currently, Rails plugins are built as gems, _gemified plugins_. They can be shared across
- different rails applications using RubyGems and Bundler if desired.
- ### Generate a gemified plugin.
- Rails ships with a `rails plugin new` command which creates a
- skeleton for developing any kind of Rails extension with the ability
- to run integration tests using a dummy Rails application. See usage
- and options by asking for help:
- ```bash
- $ rails plugin --help
- ```
- Testing your newly generated plugin
- -----------------------------------
- You can navigate to the directory that contains the plugin, run the `bundle install` command
- and run the one generated test using the `rake` command.
- You should see:
- ```bash
- 2 tests, 2 assertions, 0 failures, 0 errors, 0 skips
- ```
- This will tell you that everything got generated properly and you are ready to start adding functionality.
- Extending Core Classes
- ----------------------
- This section will explain how to add a method to String that will be available anywhere in your rails application.
- In this example you will add a method to String named `to_squawk`. To begin, create a new test file with a few assertions:
- ```ruby
- # yaffle/test/core_ext_test.rb
- require 'test_helper'
- class CoreExtTest < Test::Unit::TestCase
- def test_to_squawk_prepends_the_word_squawk
- assert_equal "squawk! Hello World", "Hello World".to_squawk
- end
- end
- ```
- Run `rake` to run the test. This test should fail because we haven't implemented the `to_squawk` method:
- ```bash
- 1) Error:
- test_to_squawk_prepends_the_word_squawk(CoreExtTest):
- NoMethodError: undefined method `to_squawk' for [Hello World](String)
- test/core_ext_test.rb:5:in `test_to_squawk_prepends_the_word_squawk'
- ```
- Great - now you are ready to start development.
- Then in `lib/yaffle.rb` add `require "yaffle/core_ext"`:
- ```ruby
- # yaffle/lib/yaffle.rb
- require "yaffle/core_ext"
- module Yaffle
- end
- ```
- Finally, create the `core_ext.rb` file and add the `to_squawk` method:
- ```ruby
- # yaffle/lib/yaffle/core_ext.rb
- String.class_eval do
- def to_squawk
- "squawk! #{self}".strip
- end
- end
- ```
- To test that your method does what it says it does, run the unit tests with `rake` from your plugin directory.
- ```bash
- 3 tests, 3 assertions, 0 failures, 0 errors, 0 skips
- ```
- To see this in action, change to the test/dummy directory, fire up a console and start squawking:
- ```bash
- $ rails console
- >> "Hello World".to_squawk
- => "squawk! Hello World"
- ```
- Add an "acts_as" Method to Active Record
- ----------------------------------------
- A common pattern in plugins is to add a method called 'acts_as_something' to models. In this case, you
- want to write a method called 'acts_as_yaffle' that adds a 'squawk' method to your Active Record models.
- To begin, set up your files so that you have:
- ```ruby
- # yaffle/test/acts_as_yaffle_test.rb
- require 'test_helper'
- class ActsAsYaffleTest < Test::Unit::TestCase
- end
- ```
- ```ruby
- # yaffle/lib/yaffle.rb
- require "yaffle/core_ext"
- require 'yaffle/acts_as_yaffle'
- module Yaffle
- end
- ```
- ```ruby
- # yaffle/lib/yaffle/acts_as_yaffle.rb
- module Yaffle
- module ActsAsYaffle
- # your code will go here
- end
- end
- ```
- ### Add a Class Method
- This plugin will expect that you've added a method to your model named 'last_squawk'. However, the
- plugin users might have already defined a method on their model named 'last_squawk' that they use
- for something else. This plugin will allow the name to be changed by adding a class method called 'yaffle_text_field'.
- To start out, write a failing test that shows the behavior you'd like:
- ```ruby
- # yaffle/test/acts_as_yaffle_test.rb
- require 'test_helper'
- class ActsAsYaffleTest < Test::Unit::TestCase
- def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
- assert_equal "last_squawk", Hickwall.yaffle_text_field
- end
- def test_a_wickwalls_yaffle_text_field_should_be_last_tweet
- assert_equal "last_tweet", Wickwall.yaffle_text_field
- end
- end
- ```
- When you run `rake`, you should see the following:
- ```
- 1) Error:
- test_a_hickwalls_yaffle_text_field_should_be_last_squawk(ActsAsYaffleTest):
- NameError: uninitialized constant ActsAsYaffleTest::Hickwall
- test/acts_as_yaffle_test.rb:6:in `test_a_hickwalls_yaffle_text_field_should_be_last_squawk'
- 2) Error:
- test_a_wickwalls_yaffle_text_field_should_be_last_tweet(ActsAsYaffleTest):
- NameError: uninitialized constant ActsAsYaffleTest::Wickwall
- test/acts_as_yaffle_test.rb:10:in `test_a_wickwalls_yaffle_text_field_should_be_last_tweet'
- 5 tests, 3 assertions, 0 failures, 2 errors, 0 skips
- ```
- This tells us that we don't have the necessary models (Hickwall and Wickwall) that we are trying to test.
- We can easily generate these models in our "dummy" Rails application by running the following commands from the
- test/dummy directory:
- ```bash
- $ cd test/dummy
- $ rails generate model Hickwall last_squawk:string
- $ rails generate model Wickwall last_squawk:string last_tweet:string
- ```
- Now you can create the necessary database tables in your testing database by navigating to your dummy app
- and migrating the database. First
- ```bash
- $ cd test/dummy
- $ rake db:migrate
- $ rake db:test:prepare
- ```
- While you are here, change the Hickwall and Wickwall models so that they know that they are supposed to act
- like yaffles.
- ```ruby
- # test/dummy/app/models/hickwall.rb
- class Hickwall < ActiveRecord::Base
- acts_as_yaffle
- end
- # test/dummy/app/models/wickwall.rb
- class Wickwall < ActiveRecord::Base
- acts_as_yaffle yaffle_text_field: :last_tweet
- end
- ```
- We will also add code to define the acts_as_yaffle method.
- ```ruby
- # yaffle/lib/yaffle/acts_as_yaffle.rb
- module Yaffle
- module ActsAsYaffle
- extend ActiveSupport::Concern
- included do
- end
- module ClassMethods
- def acts_as_yaffle(options = {})
- # your code will go here
- end
- end
- end
- end
- ActiveRecord::Base.send :include, Yaffle::ActsAsYaffle
- ```
- You can then return to the root directory (`cd ../..`) of your plugin and rerun the tests using `rake`.
- ```
- 1) Error:
- test_a_hickwalls_yaffle_text_field_should_be_last_squawk(ActsAsYaffleTest):
- NoMethodError: undefined method `yaffle_text_field' for #<Class:0x000001016661b8>
- /Users/xxx/.rvm/gems/ruby-1.9.2-p136@xxx/gems/activerecord-3.0.3/lib/active_record/base.rb:1008:in `method_missing'
- test/acts_as_yaffle_test.rb:5:in `test_a_hickwalls_yaffle_text_field_should_be_last_squawk'
- 2) Error:
- test_a_wickwalls_yaffle_text_field_should_be_last_tweet(ActsAsYaffleTest):
- NoMethodError: undefined method `yaffle_text_field' for #<Class:0x00000101653748>
- Users/xxx/.rvm/gems/ruby-1.9.2-p136@xxx/gems/activerecord-3.0.3/lib/active_record/base.rb:1008:in `method_missing'
- test/acts_as_yaffle_test.rb:9:in `test_a_wickwalls_yaffle_text_field_should_be_last_tweet'
- 5 tests, 3 assertions, 0 failures, 2 errors, 0 skips
- ```
- Getting closer... Now we will implement the code of the acts_as_yaffle method to make the tests pass.
- ```ruby
- # yaffle/lib/yaffle/acts_as_yaffle.rb
- module Yaffle
- module ActsAsYaffle
- extend ActiveSupport::Concern
- included do
- end
- module ClassMethods
- def acts_as_yaffle(options = {})
- cattr_accessor :yaffle_text_field
- self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
- end
- end
- end
- end
- ActiveRecord::Base.send :include, Yaffle::ActsAsYaffle
- ```
- When you run `rake` you should see the tests all pass:
- ```bash
- 5 tests, 5 assertions, 0 failures, 0 errors, 0 skips
- ```
- ### Add an Instance Method
- This plugin will add a method named 'squawk' to any Active Record object that calls 'acts_as_yaffle'. The 'squawk'
- method will simply set the value of one of the fields in the database.
- To start out, write a failing test that shows the behavior you'd like:
- ```ruby
- # yaffle/test/acts_as_yaffle_test.rb
- require 'test_helper'
- class ActsAsYaffleTest < Test::Unit::TestCase
- def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
- assert_equal "last_squawk", Hickwall.yaffle_text_field
- end
- def test_a_wickwalls_yaffle_text_field_should_be_last_tweet
- assert_equal "last_tweet", Wickwall.yaffle_text_field
- end
- def test_hickwalls_squawk_should_populate_last_squawk
- hickwall = Hickwall.new
- hickwall.squawk("Hello World")
- assert_equal "squawk! Hello World", hickwall.last_squawk
- end
- def test_wickwalls_squawk_should_populate_last_tweet
- wickwall = Wickwall.new
- wickwall.squawk("Hello World")
- assert_equal "squawk! Hello World", wickwall.last_tweet
- end
- end
- ```
- Run the test to make sure the last two tests fail with an error that contains "NoMethodError: undefined method `squawk'",
- then update 'acts_as_yaffle.rb' to look like this:
- ```ruby
- # yaffle/lib/yaffle/acts_as_yaffle.rb
- module Yaffle
- module ActsAsYaffle
- extend ActiveSupport::Concern
- included do
- end
- module ClassMethods
- def acts_as_yaffle(options = {})
- cattr_accessor :yaffle_text_field
- self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
- include Yaffle::ActsAsYaffle::LocalInstanceMethods
- end
- end
- module LocalInstanceMethods
- def squawk(string)
- write_attribute(self.class.yaffle_text_field, string.to_squawk)
- end
- end
- end
- end
- ActiveRecord::Base.send :include, Yaffle::ActsAsYaffle
- ```
- Run `rake` one final time and you should see:
- ```
- 7 tests, 7 assertions, 0 failures, 0 errors, 0 skips
- ```
- NOTE: The use of `write_attribute` to write to the field in model is just one example of how a plugin can interact with the model, and will not always be the right method to use. For example, you could also use `send("#{self.class.yaffle_text_field}=", string.to_squawk)`.
- Generators
- ----------
- Generators can be included in your gem simply by creating them in a lib/generators directory of your plugin. More information about
- the creation of generators can be found in the [Generators Guide](generators.html)
- Publishing your Gem
- -------------------
- Gem plugins currently in development can easily be shared from any Git repository. To share the Yaffle gem with others, simply
- commit the code to a Git repository (like GitHub) and add a line to the Gemfile of the application in question:
- ```ruby
- gem 'yaffle', git: 'git://github.com/yaffle_watcher/yaffle.git'
- ```
- After running `bundle install`, your gem functionality will be available to the application.
- When the gem is ready to be shared as a formal release, it can be published to [RubyGems](http://www.rubygems.org).
- For more information about publishing gems to RubyGems, see: [Creating and Publishing Your First Ruby Gem](http://blog.thepete.net/2010/11/creating-and-publishing-your-first-ruby.html)
- RDoc Documentation
- ------------------
- Once your plugin is stable and you are ready to deploy do everyone else a favor and document it! Luckily, writing documentation for your plugin is easy.
- The first step is to update the README file with detailed information about how to use your plugin. A few key things to include are:
- * Your name
- * How to install
- * How to add the functionality to the app (several examples of common use cases)
- * Warnings, gotchas or tips that might help users and save them time
- Once your README is solid, go through and add rdoc comments to all of the methods that developers will use. It's also customary to add '#:nodoc:' comments to those parts of the code that are not included in the public API.
- Once your comments are good to go, navigate to your plugin directory and run:
- ```bash
- $ rake rdoc
- ```
- ### References
- * [Developing a RubyGem using Bundler](https://github.com/radar/guides/blob/master/gem-development.md)
- * [Using .gemspecs as Intended](http://yehudakatz.com/2010/04/02/using-gemspecs-as-intended/)
- * [Gemspec Reference](http://docs.rubygems.org/read/chapter/20)
- * [GemPlugins: A Brief Introduction to the Future of Rails Plugins](http://www.intridea.com/blog/2008/6/11/gemplugins-a-brief-introduction-to-the-future-of-rails-plugins)